Hi, I am a beginner for haskell. I was stuck with a sample of "programming in haskell". Following is my code: --------------------------------------------------------------------- import Prelude hiding (return, fail) type Parser a = (String->[(a,String)]) return :: a -> Parser a return v = (\inp->[(v,inp)]) item :: Parser Char item = \inp -> case inp of [] -> [] (x:xs) -> [(x,xs)] failure :: Parser a failure = \inp -> [] parse :: Parser a->(String->[(a,String)]) parse p inp = p inp (>>=) :: Parser a -> (a -> Parser b) -> Parser b p >>= f = (\inp -> case parse p inp of [] -> [] [(v,out)]->parse (f v) out) p :: Parser (Char,Char) p = do x <- item item y <- item return (x,y) --------------------------------------------------------------------- But it cannot be loadded by Hug, saying: Couldn't match expected type `Char' against inferred type `[(Char, String)]' Expected type: [((Char, Char), String)] Inferred type: [(([(Char, String)], [(Char, String)]), String)] In the expression: return (x, y) In the expression: do x <- item item y <- item return (x, y) ------------------------------------------------------------------- I googled and tried a few days still cannot get it compiled, can someone do me a favor to point out what's wrong with it :-) ?